Glass Electrode Calibration for Use in the Voltammetric Determination of Stability Constants under Extreme Acidic Conditions

A glass electrode (GE) can be successfully employed to measure pH in the study of metal-ligand equilibria by voltammetry at extremely low pH (between 0 and 2); two consecutive strong acid–strong base titrations involving different base concentrations (recommended to avoid corrosion of the GE in very basic solutions) are best suited to establish the response parameters of a GE. A novel approach of using a combined linear and binomial GE calibration was developed; this procedure allows measurements between pH 0 and 2 with uncertainty better than ±0.01 pH unit. From an extensive error analysis, it has been established that the uncertainties of about ±0.5 mV in the response slope and ±1.3 mV in E° ’ might result in an absolute error in pH of about 0.02 which should not generate errors larger than 0.3 % in optimized stability constants (as log K values) determined by voltammetry at extremely low pH. A test of GE suitability for the study of metal complexes by voltammetry is also proposed; it should be imple-mented only for suspect electrodes that show response parameters outside the limits recommended in this work. KEYWORDS Glass electrode calibration, glass electrode performance, use of GE in highly acidic media, metal-ligand equilibria studies